/Engine/Plugins/FX/Niagara/Source/NiagaraEditor/Public/Toolkits/SystemToolkitModes/NiagaraSystemToolkitModeBase.h
virtual void OnActiveDocumentChanged ( [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< class [SDockTab](API\Runtime\Slate\Widgets\Docking\SDockTab) > NewActiveTab )